Shale gas is a natural gas that can be found in shale formations. To extract shale gas from shale formations, hydraulic fracturing (fracking) has been used to assist the release of the shale gas so it can be extracted to the surface for use.
Hydraulic fracturing involves injecting a fracturing fluid, which can include water mixed with sand and other chemicals, at high pressure into the shale formation containing the shale gas. The pressure of the hydraulic fluid causes the fractures in the shale rock that open to create fissures in the rock. The sand (or other proppant in the fracturing fluid) keeps the fissures open so that formation fluids, e.g. shale gas, can flow through the fractured shale formation. A production pipe is provided to the fractured shale formation, known as the production zone, and the shale gas is then extracted from the production zone to the surface through the production pipe.
In some areas, the shale formation is located below a water permeable rock layer, which may include an aquifer. It also is desirable to reduce or minimise contamination to the water in the aquifer for environmental reasons. It is desirable to reduce or minimise contamination to any other formations or areas outside the production zone for similar reasons. Further, uncontrolled leakage of shale gas may add to greenhouse gas emissions.